1. Field of the Invention
The present invention relates to a method and apparatus for controlling the thrust of an aircraft engine using a single lever power controller.
2. Related Background
A plurality of levers are required to control aircraft engines in general aviation, commercial aviation, and unmanned aircraft. For example, a throttle lever is required to control the throttle blade, a fuel mixture lever is required to control the fuel mixture, a propeller pitch lever may be required to control the RPM of the propeller or turbine fan, a waste gate lever is typically required to control the exhaust waste gate in engines which are turbo-charged, a propeller governor lever is often required to control the propeller governor, etc. The pilot is required to control all of these levers simultaneously to achieve the most efficient engine performance for the given flight conditions. This is often a hit-and-miss procedure based on the pilot's experience, and thus the engine generally is not optimized to operate in a fuel-efficient manner to produce the optimum thrust. Also, continually monitoring these many control levers increases the pilot's workload leading to pilot fatigue and reduced attention to other necessary pilot tasks. In an emergency situation, the pilot may not be able to achieve optimum engine control, leading to engine failure or loss of controlled flight. These problems are exacerbated in unmanned air vehicles (UAV's) since the pilot is remote from the aircraft and lacks sensory input regarding flight conditions.
In the field of engine control, many proposals exist for controlling the flow of fuel to the engine in accordance with detected engine operating parameters such as engine temperature, engine pressure ratio, shaft speed, etc. to maximize fuel efficiency, but such proposals fail to take into account the ambient operating conditions. Proposals of this type are described in U.S. Pat. Nos. 4,248,042; 4,551,972; 4,686,825; 5,029,778; 5,039,037; 5,277,024; and 5,613,652. However, even if such systems were adapted to aviation, the pilot would still be required to operate and continually adjust a plurality of control levers to optimize engine thrust for given flight conditions.
By 1985, it was recognized that aircraft engine efficiency is highest when the engine is run with the throttle butterfly valve fully open and the desired performance is obtained by varying propeller speed. See, for example, SAE Technical Paper Series 850895, "The Porsche Aircraft Engine PFM 3200", Helmuth Bott and Heinz Dorsch, 1985. This article proposed a single-lever control system for an aircraft engine that operates both the throttle and the propeller governor with a single lever. However, the proposed system is a mechanical linkage system which accordingly cannot optimize engine performance based on various ambient flight conditions. That is, the Porsche system may work well at a single altitude, speed, and temperature, but will seriously degrade at other flight conditions.
Thus, what is needed is a single lever power controller apparatus and a method for controlling an aircraft engine to achieve the maximum thrust efficiency throughout the flight performance envelope of the aircraft.